Field of the Invention
The present invention relates to an intermediate shaft for use in a steering column assembly, the intermediate shaft axially contracted upon receiving an impact load of above a predetermined level thereby absorbing the impact energy, and principally to a ball spline joint incorporated in the intermediate shaft for use in the steering column assembly.
In the steering column assembly of an automobile, the intermediate shaft is interposed between a steering shaft and a steering gear for transmitting a rotative operation force to the steering gear, the operation force being applied to a steering wheel.
When receiving an excessive impact at collision or the like, the intermediate shaft is contracted for impact absorption by a relative axial movement between an inner shaft and an outer shaft which are in loose-fitted relation. Furthermore, the intermediate shaft is arranged to be axially contracted in order to be mounted to the steering shaft or the steering gear when assembled in a vehicle. Moreover, the intermediate shaft is arranged to absorb vibration through expansion and contraction, vibration being produced at the steering gear, for example, when a vehicle is traveling on a bad road, thereby preventing the vibration from being transmitted to the steering shaft.
The intermediate shaft of this type incorporates therein, for example, a ball spline joint for reducing an axial sliding load. The ball spline joint comprises raceway grooves respectively formed in an inner shaft and an outer shaft and having U-shaped sectional shapes in corresponding relation, and a plurality of balls interposed between the corresponding raceway grooves and forming an array along an axial direction of the intermediate shaft.
In the typical ball spline joint, a predetermined gap is provided between an inside surface of the raceway groove and the balls in order to ensure the durability and to reduce a sliding resistance between the inner and outer shafts. The balls in the raceway groove are allowed to move by the amount of the gap. Hence, noises due to the rattling of the balls may result in some cases.
In addition, the above gap permits a rotationwise free play between the inner shaft and the outer shaft. This reduces a response performance for transmitting the rotative operation force, applied to the steering wheel, to the steering gear or causes noises due to the rattling.
An attempt has been made to reduce the rattling by using a resilient member for biasing the balls in the axial direction of the intermediate shaft. Unfortunately, an adequate effect has yet to be achieved.
In view of the foregoing, the invention has been accomplished and has an object to provide a ball spline joint free from a rotationwise rattle and noises.
For achieving the above object, a ball spline joint for interconnecting an inner shaft and an outer shaft in mutually loose-fitted relation as allowing the shafts to integrally rotate and relatively move from each other in an axial direction, the ball spline joint according to a preferred embodiment of the invention comprises raceway grooves respectively formed in the inner shaft and the outer shaft in face-to-face relation and axially extended, a plurality of balls interposed between the corresponding raceway grooves of the inner shaft and the outer shaft and forming an array in the axial direction, and a resilient member for biasing an array-end ball in an angled direction relative to the axial direction.
According to the embodiment, a stable situation of the array of balls is established by biasing the array-end ball in the angled direction relative to the axial direction, the balls individually pressed against at least either one of the raceway surfaces of the raceway grooves. This is effective to prevent an unwanted movement of the balls between the raceway grooves. As a result, the occurrence of noises can be avoided. Furthermore, a pressing force against the raceway groove is applied via the ball, such that free play (rattle) in the rotating direction can be eliminated. This ensures that the occurrence of noises due to the rattling is prevented.
In one case, the resilient member may be in contact with the array-end ball for directly biasing this ball in the angled direction. In another case, the resilient member may indirectly bias this ball in the angled direction via a spacer.